Heart failure, a syndrome characterized by impaired cardiac function, affects over five million people in the United States alone. As the most common admitting diagnosis for patients over 65, heart failure portends a worse prognosis than most cancers (Lloyd-Jones et al. (2010) Circulation 121:e46-e215). With the aging population, it is expected to affect 3.5% of the US population over the next 20 years (Heidenreich et al. (2012) Circulation 123:933-944).
Heart failure is the result of a wide variety of underlying conditions, most commonly coronary artery disease and hypertension (Ho et al. (1993) J. Am. Coll. Cardiol. 22:6A-13A), and can be associated with preserved or reduced left ventricular ejection fraction. Some patients in the low ejection fraction group exhibit a dramatic improvement with optimal medical therapy, which includes treatment with β-adrenergic receptor antagonists and inhibitors of the renin-angiotensin-aldosterone system. Why some patients have a dramatic response to pharmaceutical therapy whereas others decompensate and require transplantation is not well understood.
Candidate gene studies with targeted genotyping of common variants in ADRB1 and GRK5 members of the β-adrenergic receptor signaling pathway have shown associations with long-term heart-failure survival (Cresci et al. (2009) J. Am. Coll. Cardiol. 54:432-444; Liggett et al. (2008) Nature Medicine 14:510-517). Studies with more comprehensive genotyping of cardiovascular gene candidates identified associations between common variants in HSPB7 and FRMD4B and dilated cardiomyopathy (Stark et al. (2010) PLoS Genetics 6:e1001167) or advanced heart failure (Cappola et al. (2010) Circ. Cardiovasc. Genet. 3:147-154). In the limited number of genome-wide studies of heart failure performed (Larson et al. (2007) BMC Medical Genetics 8 Suppl. 1:S5; Smith et al. (2010) Circ. Cardiovasc. Genet. 3:256-266; Villard et al. (2011) Eur. Heart J. 32:1065-1076), the common genomic variants that have reached genome-wide significance have not been replicated in large cohorts. Genome-wide studies of improvement in left ventricular function in response to medical intervention have yet to be performed.
There remains a need for an improved therapy for patients suffering from heart failure and diagnostic biomarkers that can be used to identify patients likely to have a favorable response to medical intervention.